ash: Avoid a shutdown crash in ScreenRotationAnimation.

ash/rotator/screen_rotation_animation.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_ROTATOR_SCREEN_ROTATION_ANIMATION_H_
 #define ASH_ROTATOR_SCREEN_ROTATION_ANIMATION_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 23 matching lines @@
                           int start_degrees,
                           int end_degrees,
                           float initial_opacity,
                           float target_opacity,
                           gfx::Point pivot,
                           base::TimeDelta duration,
                           gfx::Tween::Type twen_type);
   ~ScreenRotationAnimation() override;
 
  private:
-  // Implementation of ui::LayerAnimationDelegate
+  // Implementation of ui::LayerAnimationElement:
   void OnStart(ui::LayerAnimationDelegate* delegate) override;
   bool OnProgress(double current,
                   ui::LayerAnimationDelegate* delegate) override;
   void OnGetTarget(TargetValue* target) const override;
   void OnAbort(ui::LayerAnimationDelegate* delegate) override;
 
   // The root InterpolatedTransform that defines the animation.
   std::unique_ptr<ui::InterpolatedTransform> interpolated_transform_;
 
   // The Tween type to use for the animation.
   gfx::Tween::Type tween_type_;
 
   // The initial layer opacity to start the animation with.
   float initial_opacity_;
 
   // The target layer opacity to end the animation with.
   float target_opacity_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimation);
 };
 
 }  // namespace ash
 
 #endif  // ASH_ROTATOR_SCREEN_ROTATION_ANIMATION_H_